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Poster: R Pal Date: Nov 15, 2021 5:33pm
Forum: georgeblood Subject: Re: Acoustic records recording speed

Hi Brewster,
I don't have time to do any meaningful narration right now but a video is at the link.
The video is of RCA Victor 20-30150B through an microscope depth gauge which I have used to inspect rotogravure print rollers and intaglio plates for the past 40 years. The white light is from the side of the lens and the green light is passed through a half silvered mirror from directly above. A much higher power lens is available but unless I explain what the image is it just looks like grainy images. The shiny lines are the top of the groves and the darker areas are the grove sides.
There is a lot of info in the video but I have only a few minutes.
I placed a 78 needle about 1/10th of an inch above the record and moved the focus up to see how the needle size compares to the groves. I was startled to see the rust as the needle looks clean. The focal plane is about 3 microns and it looks like the grooves are about 80 microns deep. The width measurement reticle is put away somewhere and as I wrote above I hurrying to an meeting so I don't have a groove width. I'd like to check that someday. I'd also like to make a 3d view using the measurements
Do you have any broken 78s that I could use for a side view. I sliver would help me verify the depth.

The automated speed problem discussed above needs more time and I don't have any for several weeks. The email address for this account is non-functional but thanks for the Archive.

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Poster: brewster Date: Nov 15, 2021 6:03pm
Forum: georgeblood Subject: Re: Acoustic records recording speed

So good! Yes, we have broken 78's (unfortunately)

lets connect when you have more time to figure out how to make better transfers.